Sputter deposition of materials has been widely used in the past for a number of applications including semiconductors, superconductors, and optical coatings. This sputter deposition has been accomplished through the use of DC diode sputtering, RF diode sputtering, RF magnetrun sputtering and other sputtering methods.
Typically, sputtering is accomplished by first establishing a gas discharge within a chamber. This gas discharge causes ions to be accelerated towards the cathode and eventually collide with the cathode surface. This collision with the cathode surface causes ion particles to be released from that surface and deposited on other surfaces in close proximity to the cathode. A substrate is typically placed close to the cathode and thus can be coated with the ion particles released from the cathode.
Magnetron sputtering is achieved by placing a magnet assembly behind the cathode. This magnet assembly can contain the plasma that is created by the gas discharge. Control of the plasma is very beneficial since it often maximizes the use of the cathode surface. By varying the design and configuration of the magnet assembly, depletion of the target surface can thus be controlled and maximized. In a typical gas discharge a plasma is created directly in front of the cathode. The plasma typically takes on an overall positive charge. A space is created between the plasma and the cathode surface which is free from electric charge. When electrons collide with the cathode surface, occasionally negatively charged ions are released. These negatively charged ions are accelerated across the dark space toward the plasma, due to the charge of the plasma. Subsequently the ions are accelerated through the plasma and collide with any objects that are situated behind this plasma. Due to the high rate of acceleration and large amount of energy, these ions can cause destruction or disturbance to a coated surface when they collide with that surface.
Sputter deposition is often used to produce high quality optical mirrors. When sputtering is used for this purpose, alternating layers of thin films are required to be deposited on a substrate. Therefore, it is necessary to sputter a first material to a certain thickness upon a substrate, and subsequently sputter a second material to a desired thickness on the same substrate. This sequence is then repeated for as many times as desired.
The need for alternating layers of sputtered material creates a problem in typical sputtering apparatus. The different materials must be sputtered onto the same substrate without unnecessarily handling the substrates themselves. Also, constant handling and changing of the target material is undesirable since that requires opening and closing of the gas filled chamber.
One approach has been to have numerous targets within one chamber and position the substrate in front of the appropriate target. While this method does allow for alternating coatings, the problem of direct, high energy collisions still exists. Additionally, the number of mirrors that can be produced concurrently is limited.